Lucky you! My Christmas break was blessed with my step-daughter being sent to us, with a head-full of them! Yeah, that was one nice present from Santa (DH's ex-wife).
It was my second time to deal with them. As far as preventing them, I don't have any advice the others haven't already mentioned, although I disagree with using the pesticide on your child's hair, with no sign of lice being present. The stuff is too dangerous, and lice are already becomming immune to the products on the market.
My youngest daughter got them, after spending the night at a neighbor's house. They never did tell me that their daughter had them. I found out after the fact, because ANOTHER neighbor's daughter got the too, after staying over at this particular girl's house.
That was the lice case from he**. Rid didn't work and she had to sleep with mayo in her hair, under a shower cap, for a WEEK. To this day, she gags if she smells mayo. I had to sit and nit pick for almost two weeks before we got them all. Did I mention that DD had wavy, thick, blond hair? They were soooo hard to see.
Stepdaughter's case wasn't as bad. Rid worked and I managed to get all of the nits in one sitting. I was shocked. I was stocked up with mayo and shower caps, preparing for the worst.
Research the life cycle of lice and you'll be better prepared to find them. Good luck!